Major Facilitators

Major Facilitators are membrane proteins that help with both influx and outflux of specific small molecules. They are neither passive channels, nor do they active pumping, like the ATPases. Like a rocker-switch, they tilt between the two states 'outside open' and 'inside open'. This tilting (or switching) is triggered when a molecule has docked inside, and it transports the molecule to the other side. There are major facilitator uniporters, symporters, and antiporters. Antiporters usually transport a second, different, molecule, when switching back in the opposite direction. In 2009, there is still no structure data that would clearly show the transport process in major facilitators.

Classification
TCDB, the most sophisticated classification of transport proteins to date, classifies the major facilitators as family 2.A.1 in the clan of secondary active porters.

Available structures
The family has about 10,000 sequenced members from all living organisms. There are, however, only a few protein structures resolved.
 * from E. coli K12:
 * the glycerol-3-phosphate transporter (1pw4)
 * the multidrug resistance protein EmrD (2gfp)
 * the lactose permease (1pv7, 2cfp, 2cfq, 2v8n)
 * from Clostridum phytofermentans: the sugar transporter (3brs)

Weblinks

 * The TCDB database
 * TCDB: 2.A.1 The Major Facilitator Superfamily (MFS)
 * TCDB: Transport proteins with PDB structures